Ion implantation is able to implant exact doses of ions in a controllable doping profile in a semiconductor wafer. Thus ion implantation has largely supplanted methods such as diffusion to manufacture devices in semiconductor wafers as the number of devices on each wafer has vastly increased (VLSI) and the feature sizes of the devices has become much smaller. Ion implantation can effect more accurate doses of the desired ions, and can exert closer control over doping profiles. Ion implantation equipment accordingly has also become more sophisticated. However, several problems remain to be addressed.
Ion implantation operates on only one wafer at a time, or on one batch of wafers on a carousel. Openings in a photoresist layer on the wafer are made where ions of a particular chemical species are to be implanted. The ion beam carrying the desired ions strikes the patterned wafer, implanting ions into the wafer in the openings in the photoresist. The photoresist acts as a stop everywhere else. In order to make devices such as CMOS devices and the like, after the first implantation is performed and the wafer is removed from the ion implanter, the photoresist is removed, a new layer of photoresist put down, repatterned to provide openings where different chemical ion species are to be implanted, and the ion implantation repeated with a different beam of ions. In order to make complex circuits, this process may be repeated several times to complete devices on a single wafer or batch of wafers.
Thus it is apparent that improving the throughput speed of the ion implantation process can save time for each implant, thereby reducing costs considerably. Means of increasing the throughput of ion implantation, without, however, sacrificing the quality of the resultant devices, would be highly desirable.